I think the best advice I could give is to treat every inquiry as legitimate, no matter what your suspicion may be. Bad news travels a lot faster than good news in the online business world, so you need to be taking every precaution to mitigate as much bad news getting out just to come close to balancing the good news with it.
Things like poor customer response rates seriously irritate retailers and can lead to a lot of complaints in all the wrong places, like trading forums such as SaleHoo.
Will every inquiry be genuine? ... absolutely not. In fact, I would suggest over 50% may well be a complete waste of time, but treating every inquiry as a priority, not matter if it is a waste of time of not is the price of doing GOOD business in this marketplace of online trading.
If you get a message that needs clarifying, simply ask for the clarification that you need to respond in an informative and prompt manner and it's going to be extremely difficult for anyone to be able to have anything negative to say about your level of Customer Service and GREAT Customer Service is a great place to start building a brand's reputation.
As a supplier, always put yourself in the customer's place and serve them as you, yourself, would like to be served and it's hard to go wrong from there :)